Abrupt field-induced transition triggered by magnetocaloric effect in phase-separated manganites

The occurrence at low temperatures of an ultrasharp field-induced transition in phase separated manganites is analyzed. Experimental results show that magnetization and specific heat step-like transitions below 5 K are correlated with an abrupt change of the sample temperature, which happens at a certain critical field. This temperature rise, a magnetocaloric effect, is interpreted as produced by the released energy at the transition point, and is the key to understand the existence of the abrupt field-induced transition. A qualitative analysis of the results suggests the existence of a critical growing rate of the ferromagnetic phase, beyond which an avalanche effect is triggered.Comment: 6 pages, 4 figures included. Acepted for publication in Phys. Rev.

Attachment of Staphylococcus epidermidis RP62A to chemically modified cellulose derivatives

Coagulase negative staphylococci, most notably Staphylococcus epidermidis, have been identified as a predominant cause of cardiovascular implant infection, which begins with the colonization of the device by the bacteria. One possible approach to reduce this event is to understand how the physicochemical properties of bacterial surface influence attachment to biomaterials. In the present study, the attachment of coagulase negative Staphylococcus epidermidis expressing capsular polysaccharide/adhesin (PS/A), the most common etiological agent of colonization of implantable medical devices, was assessed in vitro to cellulose diacetate (CDA), to CDA chemically modified by de-acetylation (CDA-D) and by phosphorylation (CDA-P), as well as to reference Low Density Polyethylene (LDPE). The quantification of S. epidermidis attached to cellulose diacetate (CDA) in phosphate buffer saline (PBS) elicited information regarding the interaction between the bacterial strain and the polymeric biomaterial. There was a significant difference in the adhesion of RP62A to CDA, compared to LDPE. Chemical modifications of CDA by de-acetylation and by phosphorylation were effective in lowering bacterial attachment. These chemical treatments increased the acidic parameter of the surface energy and decreased the acid-base interactions with acidic sites of the capsular PS/A. In other terms, these treatments also promoted a decrease in hydrophobicity that linearly correlates with a decrease in the number of attached cells

Effects of Fe doping in La1/2Ca1/2MnO3

The effect of Fe doping in the Mn site on the magnetic, transport and structural properties of polycrystalline La1/2Ca1/2MnO3 was studied. Doping with low Fe concentration (< 10%) strongly affects electrical transport and magnetization. Long range charge order is disrupted even for the lowest doping level studied (~2%). For Fe concentration up to 5% a ferromagnetic state develops at low temperature with metallic like conduction and thermal hysteresis. In this range, the Curie temperature decreases monotonously as a function of Fe doping. Insulating behavior and a sudden depression of the ferromagnetic state is observed by further Fe doping.Comment: 2 pages, presented at ICM2000, to appear in JMM

Friction and wear behaviour of bacterial cellulose against articular cartilage

Bacterial cellulose (BC) is a natural and biocompatible material with unique properties, such as high water holding capacity, ultra-fine fibre network and high strength that makes it an attractive material for the repair of articular cartilage lesions. However, data on the tribological properties of BC is very scarce, particularly if natural articular cartilage is involved in the contact. In this work, unmodified BC pellicles were grown from Gluconacetobacter xylinus in order to be used as tribological samples against bovine articular cartilage (BAC) in the presence of phosphate buffered saline (PBS). The tribological assessment of the sliding pairs was accomplished using reciprocating pin-on-flat tests at 37ºC. The reciprocating sliding frequency and stroke length were kept constant at 1 Hz and 8 mm, respectively. Contact pressures ranging from 0.80 to 2.40 MPa were applied. The friction coefficient evolution was continuously monitored during the tests and the release of total carbohydrates into the lubricating solution was followed by means of the phenol-H2SO4 method as an attempt to evaluate wear losses. The morphology of worn surfaces was characterized by SEM/EDS and the main wear mechanisms were identified. Low friction coefficient values (~ 0.05) combined with the preservation of the mating surfaces (BC and BAC) indicate the potential of BC to be used as artificial cartilage for articular joints.Fundação para a Ciência e a Tecnologia (FCT

Molecularly imprinted intelligent scaffolds for tissue engineering applications

The development of molecularly imprinted polymers (MIPs) using biocompatible production methods enables the possibility to further exploit this technology for biomedical applications. Tissue engineering (TE) approaches use the knowledge of the wound healing process to design scaffolds capable of modulating cell behavior and promote tissue regeneration. Biomacromolecules bear great interest for TE, together with the established recognition of the extracellular matrix, as an important source of signals to cells, both promoting cellâ cell and cellâ matrix interactions during the healing process. This review focuses on exploring the potential of protein molecular imprinting to create bioactive scaffolds with molecular recognition for TE applications based on the most recent approaches in the field of molecular imprinting of macromolecules. Considerations regarding essential components of molecular imprinting technology will be addressed for TE purposes. Molecular imprinting of biocompatible hydrogels, namely based on natural polymers, is also reviewed here. Hydrogel scaffolds with molecular memory show great promise for regenerative therapies. The first molecular imprinting studies analyzing cell adhesion report promising results with potential applications for cell culture systems, or biomaterials for implantation with the capability for cell recruitment by selectively adsorbing desired molecules.The authors wish to thank Dr. Julia Vela-Ramirez, Ms. Heidi Culver, and Mr. John Clegg for important discussions and suggestions. This work was supported in part by the University of Texas-Portugal Collaborative Research Program, and the Grant UTAP-ICDT/CTM-BIO/0023/2014. M.E.W. is supported by a National Science Foundation Graduate Research Fellowship

In-situ forming silk sericin-based hydrogel for chronic wound healing

info:eu-repo/semantics/publishedVersio

Noncollinear magnetic ordering in small Chromium Clusters

We investigate noncollinear effects in antiferromagnetically coupled clusters using the general, rotationally invariant form of local spin-density theory. The coupling to the electronic degrees of freedom is treated with relativistic non-local pseudopotentials and the ionic structure is optimized by Monte-Carlo techniques. We find that small chromium clusters (N \le 13) strongly favor noncollinear configurations of their local magnetic moments due to frustration. This effect is associated with a significantly lower total magnetization of the noncollinear ground states, ameliorating the disagreement between Stern-Gerlach measurements and previous collinear calculations for Cr_{12} and Cr_{13}. Our results further suggest that the trend to noncollinear configurations might be a feature common to most antiferromagnetic clusters.Comment: 9 pages, RevTeX plus .eps/.ps figure